linux-kernel - [PATCH v6 05/12] drm/panfrost: Check sgt to know whether pages are already mapped

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Message-ID: <20251015000930.356073-6-adrian.larumbe@collabora.com>
Date: Wed, 15 Oct 2025 01:09:11 +0100
From: Adrián Larumbe <adrian.larumbe@...labora.com>
To: linux-kernel@...r.kernel.org
Cc: dri-devel@...ts.freedesktop.org,
	Steven Price <steven.price@....com>,
	Boris Brezillon <boris.brezillon@...labora.com>,
	kernel@...labora.com,
	Adrián Larumbe <adrian.larumbe@...labora.com>,
	Rob Herring <robh@...nel.org>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>
Subject: [PATCH v6 05/12] drm/panfrost: Check sgt to know whether pages are already mapped

In the MMU's page fault ISR for a heap object, determine whether the
faulting address belongs to a 2MiB block that was already mapped by
checking its corresponding sgt in the Panfrost BO.

This is done in preparation for a future commit in which the MMU mapping
helper might fail, but the page array is left populated, so this cannot
be used as a check for an early bail-out.

Signed-off-by: Adrián Larumbe <adrian.larumbe@...labora.com>
---
 drivers/gpu/drm/panfrost/panfrost_mmu.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
index cf272b167feb..ba32d99ed854 100644
--- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
+++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
@@ -600,10 +600,12 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
 		refcount_set(&bo->base.pages_use_count, 1);
 	} else {
 		pages = bo->base.pages;
-		if (pages[page_offset]) {
-			/* Pages are already mapped, bail out. */
-			goto out;
-		}
+	}
+
+	sgt = &bo->sgts[page_offset / (SZ_2M / PAGE_SIZE)];
+	if (sgt->sgl) {
+		/* Pages are already mapped, bail out. */
+		goto out;
 	}
 
 	mapping = bo->base.base.filp->f_mapping;
@@ -625,7 +627,6 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
 		}
 	}
 
-	sgt = &bo->sgts[page_offset / (SZ_2M / PAGE_SIZE)];
 	ret = sg_alloc_table_from_pages(sgt, pages + page_offset,
 					NUM_FAULT_PAGES, 0, SZ_2M, GFP_KERNEL);
 	if (ret)
-- 
2.51.0